The hypothesis of this study is that concentrated infant formula will significantly improve growth and lymphocyte counts, reduce opportunistic infections, and improve the quality of life in HIV-infected infants. The purpose of this multicenter ACTG study is to evaluate the effect of concentrated (25.7 kcal/oz) infant formula compared with standard (20 kcal/oz) infant formula on weight gain, body composition, immunologic and virologic status, quality of life, and dietary intake in HIV-infected infants from birth to 6 months. Infants will be randomized in a double-blinded design to receive either 25.7-or 20-kcal/oz infant milk-based formula ad libitum. All infants will remain on blinded treatment assignment until the 8 week study visit (56+/- 14 days). At that time, HIV-infected infants will continue on study, while the majority of infants determined to be uninfected will come off the study. A smaller group, approximately 11% of HIV-exposed but uninfected infants will receive standard (20 kcal/oz) infant formula and will serve as a comparison group for the infected infants who receive standard formula. Infants will be monitored by the primary endpoints: weight, length, and weight for length; and the secondary endpoints: head circumference, CD3+CD4+ and CD3+CD8+ counts, opportunistic infections, tolerability of formula, and quality of life assessments.